Known punches of this type generally comprise a stationary base plate from which two upstanding side supports project. The side supports are sometimes integrally formed with the base plate, but are more often in the form of separate mirror image brackets welded to the base plate. Respective cylindrical cutting tools with downwardly directed cutting edges are mounted in the side supports and are axially movable against spring force upon depression of a handle or press bar which is pivotally connected between the side supports. When the press bar is actuated the tools are simultaneously pushed downwards so that their cutting edges co-operate with respective apertures in the base plate to cut holes in any sheets of paper inserted into a throat area between the side supports and the base plate.
Although two cutting tools are most common in punches of this type, any desired number may be provided. Moreover, three-or four-tool punches are particularly common in countries such as France, Sweden and U.S.A. to cut holes to correspond with standard binders used in those countries.
In addition to the variation in the number of cutting tools, the spacing between the respective cutting tools may vary to match the spacing of fastening means in different types of loose-leaf binders. In all, about nine different sizes of punch are currently on the market to cater for the varying requirements.
At present, the main structural components for punches of the type just described, namely the base plate, the side support brackets and the press bar, are individually cast or otherwise fabricated from mild steel. In addition, a tray moulded from plastics material is usually fitted to the underside of the base plate to retain the waste cuttings. Although the aforesaid mild steel construction gives the punch the necessary strength for cutting through several mm of paper, the cost of tooling up for fabricating components for one size of punch (i.e. one particular cutting tool spacing) amounts to many thousands of pounds. The cost of obtaining a mould for the tray is also very expensive. Accordingly, many manufacturers do not produce less popular punch sizes because it is not economically feasible to do so.
It is an object of the present invention to propose a novel design of punch which will allow manufacture by less expensive methods and with materials of less inherent strength than hitherto.